Automotive Scan Tool and Diagnosis

This is a short article on how to pick out the right automotive scan
tool based on needs and why you might want a scanner instead of just a code
reader. The difference is, scanners can read the data stream. See what these cost effective tools can and cannot do. Discover
how to use it properly to diagnose some of the most common generic codes found set in memory.

At the bottom of this short page is a link
to pictures and reviews of scanners I own. I picked the Equus 3040 on
the right as a good compromise between cost and features. Also on this
page is a discussion about common oxygen sensor codes, diagnosis tips and a video showing how to replace an o2 if it's needed.

Connecting the diagnostic tool
to a vehicle, pulling out the codes and then resetting the light
is one of your auto repair shops favorite jobs. They don't have to get dirty, bust their knuckles and it pays well. Some charge a flat rate diagnostic fee of 1 hour for this operation. Although, many shops will apply this to any repairs purchased.

Code Reader Type Scan Tools

For as little as $20 you can have your own automotive code reader. Many
offer 1 or 2 button operation and aren't that hard to figure out for
home use. This means you can perform initial diagnosis when the
service engine soon light or check engine light comes on.

I would like to mention that most of the scan tools and code readers
today come with an in-depth operation manual and a money back
guarantee. This leaves little to worry about in terms of learning curves
or waste of working capital. The manuals will explain how to pull and erase
codes plus offer information on what it stands for.

As I
mentioned in a few previous articles, sometimes codes are intermittent
and clearing or erasing them is all that needs to be done to keep
the light off for good. If you erase and it immediately comes
back or returns in 24 hours of operation this is a hard
failure. Here's an example of a hard code.

For this example of automotive scan tool operation and reading the
comprehensive data I'll give you a very common code that you just might
find set in the automobile computer memory some day.

I come across the oxygen sensor
voltage low or high code all the time. Many mechanics when they find
this code just want to go ahead and replace the oxygen sensors. This may not be the right move.

When
you pull this code up on your automotive scan tool, the first thing you
want to do is reset it and see if it returns. If the warning lamp comes back on and the code has reset the second thing you do is read the data stream for the oxygen sensors.

Reading
scan tool data for this code using the collected information from the
cars main computer is easier then many would think. If you have an Actron scanner that can view the data stream you can record the information in snap shot mode or run the specialized O2 monitor test mode.

oxygen sensor operation

The oxygen sensor voltage should vary quickly from about 200 to 800
mV. The rule of thumb is that the voltage should go below 500, and above
500 mV in an even pattern.

This is known as o2 cross counts.
This is how many times the voltage crosses the middle specification of
500mv. If you see an oxygen sensor that has a fixed voltage or a voltage
that is always below 500. You want to check the wiring to the sensor.
The oxygen sensor wiring is underneath the vehicle and is easily damaged
by road debris.

Another reason you may have a low or fixed voltage is the
oxygen sensor is reading correctly, but the exhaust gases are not in the
proper range. This could relate to a problem in the fuel
management program.

Meaning the exhaust gases are actually lean or rich
due to a failure of a fuel system component. A prime example example
would be a leaky fuel injector, vacuum leak, or misfire condition. To
clarify my point, if you set an o2 code this does not always indicate the sensors need to be replaced. What these codes do indicate is diagnosis is necessary.

When Do Oxygen Sensors Need Replacing

The exception to this rule is if an automobile has extremely high
mileage. Oxygen sensors can start to lose their accuracy at around
100,000 miles. Again, this doesn't mean
the sensor needs to be replaced, but it's an indication sensor
operation should be checked carefully.

Using the automotive scan
tool can be interesting and fun. Reading data can be a great
learning experience. Another bonus is plugging in and
reading the data is a clean job. It won't cover you with
grease, no knuckle busting and it's almost impossible to
injure yourself performing the operation. Bookmark and share this diagnostic page after watching the video.

I own a wide variety of automotive scanners
for home and professional usage. See the ones I own plus a comparison
of the features and benefits of each. The next link takes you to reviews of automotive scan tools.

My first page about this subject provides a
few more common reasons the check engine light might pop on. Go to the
page about auto scan tools.

This article is a little more advanced and requires an advanced scan tool that can read the data stream. Learn more about
reading scan tool data.

Up next is the about us page. Find out more about the car mechanic that built this website and find more ways to get car questions answered.

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